Ed Lantz provided a survey of large-scale immersive displays as published by ACM SIGGRAPH in the Emerging Display Technology Conference Proceedings, August, 2007. Wrap-around cylindrical or dome screens are said to be preferred over rectilinear immersive screens in cinematic applications as they provide a more seamless appearance over a greater range of viewing angles and conditions.
There are specific problems in providing a back-projection screen e.g. for a simulator which is basically spherical in shape (spheroidal) as shown schematically in FIG. 1 or has a significant angular extent e.g. more than 180°, e.g. a half sphere or half cylinder screen. Outside a translucent spherical (truncated spherical) screen 2, projectors 4 are arranged to project the images required for the simulator onto the screen 2. The images from the projectors overlap so that care needs to be taken at the overlap positions so that the images remain realistic and are not subject to distortions.
The screen operates in back projection for which a diffusing screen is required. Although diffusing flat back projection screens are known, these are not so easily adapted for spherical use. One problem with viewing inside a spherical dome is that light from one side of the screen will impinge on the other. This differs from the flat screen for which the only light projected onto the screen is that from ambient light sources and that can be reduced by suitable shading within the enclosure where the simulator is located. But for the spherical screen it is the image itself on one side of the screen which becomes the ambient light for the image on the other side. This effects the contrast that can be obtained and renders materials suitable for flat screens to be not suitable for spherical screens if the same levels of contrast are to be achieved.
At present there are no commercial diffusers that combine all the conflicting requirements for spherical screens. Some diffusers have a broad HGA at the expense of sharpness. Other diffusers have excellent sharpness at the expense of speckle. Even other diffusers have a very good balance of transmissive/reflective gain, which ensures a high image brightness and high contrast but at the expense of transmissive half gain angle.